CN118974624A

CN118974624A - Piezoelectric motor and control method thereof

Info

Publication number: CN118974624A
Application number: CN202280094400.6A
Authority: CN
Inventors: 有贺弘; 荣一骑; 服部和广; 二瓶泰英; 松井拓未; 张富伟
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Filing date: 2022-03-31
Publication date: 2024-11-15

Abstract

For a piezoelectric actuator for driving a driven element linearly by inducing elliptical motion in a vibrating element by vibration of the piezoelectric element, a driving apparatus is provided which improves control at very low speeds and/or is capable of using a smaller boost circuit to provide the driving voltage of the piezoelectric actuator. According to one embodiment, a driving apparatus for driving a driven element in an axial direction is provided. The driving apparatus includes: a piezoelectric actuator, wherein the piezoelectric actuator includes a vibration element in contact with a driven element and one or more groups of piezoelectric elements attached to the vibration element; and a controller, wherein each group of piezoelectric elements includes one or more piezoelectric elements, in each group of piezoelectric elements, a first electrode for expanding or contracting a first region of the piezoelectric elements in the group of piezoelectric elements and a second electrode for expanding or contracting a second region of the piezoelectric elements in the group of piezoelectric elements are disposed along the axial direction, wherein in each group of piezoelectric elements, a common third electrode or a separate third electrode paired with the first electrode and the second electrode is disposed such that the vibration element of the piezoelectric actuator has: a bending mode in which a middle portion in the axial direction becomes convex or concave, so that end portions of the vibration element move in the axial direction at both ends in the axial direction; an expansion/contraction mode in which one end portion at both ends of the axial direction expands/contracts and the other end portion expands/contracts with time in opposite phases, whereby the end portion of the vibration element moves in a direction perpendicular to the axial direction. The controller is configured to vibrate the vibration element by applying an oscillating voltage signal of the same frequency to the first electrode and the second electrode, thereby driving the driven element in contact with the vibration element in the axial direction. Generating vibrations of a first mode based on the bending mode in the vibration element when the oscillating voltage signals applied to the first electrode and the second electrode are in phase; when the oscillating voltage signals applied to the first electrode and the second electrode are in opposite phases, a vibration of a second mode based on the expansion/contraction mode is generated in the vibration element, wherein the controller is configured to control a speed of the driven element by controlling a phase difference between the voltage signal applied to the first electrode and the voltage signal applied to the second electrode. Another aspect of the present invention provides a compact boost circuit for providing a drive voltage for a piezoelectric actuator.

Description

Piezoelectric motor and control method thereof

Technical Field

The present application relates to the field of piezoelectric actuators, and more particularly to a driving apparatus (also referred to as a piezoelectric motor) that drives a driven element using a piezoelectric actuator, and a method of controlling such a driving apparatus.

Background

Today, a general camera is equipped with an auto-focusing mechanism. The auto-focus mechanism is used to focus an object by adjusting an optical distance from the lens unit to the image sensor. The lens unit is generally driven by an actuator.

In recent years, there is an increasing demand for telephoto imaging or moving picture imaging using a camera mounted on a portable device such as a smart phone. Telephoto imaging requires a longer focal length, while auto-focusing requires a stroke of the lens unit actuator of more than 1mm. Since the movable parts are heavier than before, a greater thrust is required to move these heavy parts. For static imaging, high power is required to move the movable part rapidly. On the other hand, for moving picture imaging, the actuator needs to be controlled at a very low speed, thereby causing the lens unit to start moving smoothly from a stationary state or stop moving smoothly.

The actuator typically used in portable devices such as smartphones is a linear VCM (voice coil motor), whereas piezoelectric actuators used in larger single lens reflex cameras have the advantage of high energy density and high power despite their small size.

Disclosure of Invention

A piezoelectric actuator has been proposed for linearly driving a driven element (e.g., a shaft or some other body) by vibrating a piezoelectric element such that the vibrating element generates an elliptical motion. However, for some such piezoelectric actuators, it is difficult to control at very low speeds. Further, since the piezoelectric actuator requires a high voltage (for example, 40V to 100V), in order to integrate the piezoelectric actuator in a portable device such as a smart phone (typically, operating at a voltage of about 3V), a step-up device (a device for increasing the voltage) is required, and further, a smaller size of such a step-up device is desired.

The present application solves the above-mentioned problems.

A first implementation of the first aspect of the present application provides a driving apparatus for driving a driven element in an axial direction, the driving apparatus comprising: a piezoelectric actuator, wherein the piezoelectric actuator includes a vibration element in contact with a driven element and one or more groups of piezoelectric elements attached to the vibration element; a controller, wherein each group of piezoelectric elements includes one or more piezoelectric elements, in each group of piezoelectric elements, a first electrode for expanding or contracting a first region of the piezoelectric elements in the group of piezoelectric elements and a second electrode for expanding or contracting a second region of the piezoelectric elements in the group of piezoelectric elements are disposed along the axial direction, wherein in each group of piezoelectric elements, a common third electrode or a separate third electrode paired with the first electrode and the second electrode is disposed, such that the vibration element of the piezoelectric actuator has: a bending mode in which a middle portion in the axial direction becomes convex or concave, so that end portions of the vibration element move in the axial direction at both ends in the axial direction; an expansion/contraction mode in which one end portion at both ends of the axial direction expands/contracts and the other end portion expands/contracts with time in opposite phases, whereby the end portion of the vibration element moves in a direction perpendicular to the axial direction, wherein the controller is configured to vibrate the vibration element by applying an oscillating voltage signal of the same frequency to the first electrode and the second electrode, thereby driving the driven element in contact with the vibration element in the axial direction, wherein vibration of a first mode based on the bending mode is generated in the vibration element when the oscillating voltage signals applied to the first electrode and the second electrode are in phase; when the oscillating voltage signals applied to the first electrode and the second electrode are in opposite phases, a vibration of a second mode based on the expansion/contraction mode is generated in the vibration element, wherein the controller is configured to control a speed of the driven element by controlling a phase difference between the voltage signal applied to the first electrode and the voltage signal applied to the second electrode.

According to the feature of this implementation, namely, by driving the driven element using vibration based on the bending mode and vibration based on the expansion/contraction mode, and controlling the speed of the driven element by controlling the phase difference between the voltage signal applied to the first electrode and the voltage signal applied to the second electrode, the vibration element vibrates in the direction perpendicular to the pushing force even when the phase difference is substantially pi and there is no pushing force. Therefore, friction generated between the vibration element and the driven element is dynamic friction. This can avoid problematic behavior in that when starting to move the driven element, switching from stiction to dynamic friction causes the driven element to suddenly start moving, or the driven element suddenly stops due to switching from dynamic friction to stiction. Thus, the movement improves the linearity of the movement with respect to the control signal.

According to a second implementation of the first aspect of the present application based on the first implementation of the first aspect of the present application, the voltage signal is applied to the first electrode and the second electrode to make the end portion of the vibration element perform an elliptical motion, the elliptical motion being a combination of a vibration component in the axial direction and a vibration component perpendicular to the axial direction, and the controller is configured to control a vibration amplitude of the vibration component in the axial direction and a vibration amplitude of the vibration component perpendicular to the axial direction by controlling the phase difference.

According to this implementation, the vibration of the vibrating element generates a thrust on the driven element in an advantageous manner.

According to a third implementation of the first aspect of the present application based on the first or second implementation of the first aspect of the present application, the vibration element includes a hole, the driven element includes a cylindrical shape, and the driven element inserted into the hole is driven in the axial direction.

According to this implementation, the axis of the driven element can be stabilized.

According to a fourth implementation form of the first aspect of the application as such or as based on any of the first to third implementation forms of the first aspect of the application, the one or more sets of piezoelectric elements attached to the vibration element comprise two or more sets of piezoelectric elements attached in symmetrical positions with respect to the vibration element, the same voltage signal being applied to the first electrode of each piezoelectric element, the same voltage signal being applied to the second electrode of each piezoelectric element.

According to this implementation, the driven element may be driven by forces balanced about the axis.

According to a fifth implementation form of the first aspect as such or as claimed in any of the first to fourth implementation forms of the first aspect, the controller is configured to make the phase difference substantially pi so that the speed of the driven element is zero.

According to this implementation, since the vibration element vibrates in the direction perpendicular to the thrust even when the phase difference is pi and there is no thrust, friction between the vibration element and the driven element is dynamic friction, and the driven element is substantially in a stationary state (does not make axial movement).

According to a sixth implementation of the first aspect of the present application based on any of the first to fifth implementation of the first aspect of the present application, the controller is configured to gradually decrease or increase the phase difference from substantially pi when starting to drive the driven element from zero speed, and/or the controller is configured to gradually approach the phase difference to approximately pi when setting the speed of the driven element to zero.

According to this implementation, the speed of the driven element can be adjusted by gradually changing the phase difference.

According to a seventh implementation form of the first aspect of the application as such or as based on the second implementation form of the first aspect of the application, the controller is further configured to control the amplitude of the voltage signals applied to the first and second electrodes to compensate for amplitude variations of the vibration component perpendicular to the axial direction caused by the control of the phase difference.

According to this implementation, when the phase difference between the voltage signals applied to the first electrode and the second electrode is changed to control the speed of the driven element, the amplitude of the vibration component perpendicular to the axial direction can be kept constant.

According to an eighth implementation of the first aspect of the present application based on any of the first to seventh implementation of the first aspect of the present application, the controller is configured to control the speed of the driven element by further controlling the frequency and/or amplitude of the voltage signals applied to the first and second electrodes.

According to this implementation, a larger speed variation of the driven element can be achieved than by merely changing the phase difference between the voltage signals applied to the first electrode and the second electrode.

According to a ninth implementation of the first aspect of the present application based on any of the first to seventh implementation of the first aspect of the present application, the controller is configured to control the speed of the driven element by controlling a frequency and/or an amplitude of the voltage signal applied to the first electrode and the second electrode, not a phase of the voltage signal, when the speed of the driven element is equal to or greater than a predetermined value.

According to this implementation, when the speed control is not required at a low speed, the speed of the driven element can be efficiently adjusted by controlling the frequency and/or amplitude of the voltage signals applied to the first electrode and the second electrode.

According to a tenth implementation form of the first aspect as such or as based on any of the first to ninth implementation forms of the first aspect of the application, the voltage signal applied to the first and second electrodes is a square wave, a triangular wave, a sawtooth wave or a sine wave.

According to at least some options of this implementation, digital control of the voltage signals applied to the first and second electrodes may be facilitated.

According to an eleventh implementation form of the first aspect as such or as any of the first to tenth implementation forms thereof, the driving apparatus further comprises a boost circuit for converting a voltage of the power supply into a voltage for driving the piezoelectric actuator.

According to this implementation, the piezoelectric actuator can be driven even when the power supply voltage (e.g., the power supply voltage of the portable device) is lower than the voltage required to drive the piezoelectric actuator.

According to a twelfth implementation of the first aspect of the present application based on the eleventh implementation of the first aspect of the present application, the boost circuit comprises a driver for providing a voltage to the piezoelectric actuator through an external inductor.

According to a thirteenth implementation form of the first aspect of the application as such or based on the twelfth implementation form of the first aspect of the application, the piezoelectric actuator is represented by an equivalent circuit comprising an internal R-L-C (resistor-inductor-capacitor) series resonant circuit and a parallel connected capacitive component, the resonant frequency of the R-L-C series resonant circuit consisting of the output impedance of the driver, the external inductor and the capacitive component of the piezoelectric actuator substantially matching the resonant frequency of the internal R-L-C series resonant circuit of the piezoelectric actuator.

According to this implementation, the energy of the oscillating voltage signal is efficiently transferred to the vibration of the vibration element of the piezoelectric actuator.

According to a fourteenth implementation form of the first aspect as such or as based on any of the first to thirteenth implementation forms of the first aspect, the parameters of the internal R-L-C series resonant circuit of the piezoelectric actuator are adjusted such that the inductance of the external inductor is 30 μh or less.

According to this implementation, the size of the external inductor is relatively small, which makes the external inductor suitable for inclusion into a portable device. Furthermore, small inductances can be achieved by circuit parameter designs within the piezoelectric actuator without the need to introduce additional elements.

According to a fifteenth implementation form of the first aspect as such or based on any of the first to thirteenth implementation forms of the first aspect, the booster circuit has an external capacitor connected in parallel with the capacitance component of the piezoelectric actuator such that an inductance of the external inductor is 30 μh or less.

According to this implementation, the size of the external inductor is relatively small, which makes the external inductor suitable for inclusion into a portable device. Furthermore, small inductances can be achieved by adding external elements without changing the circuit parameter design within the piezoelectric actuator.

According to a second aspect of the present application, there is provided a driving apparatus comprising: a piezoelectric actuator including a vibration element and one or more sets of piezoelectric elements attached to the vibration element; and a controller. Each group of piezoelectric elements includes one or more piezoelectric elements in each group of piezoelectric elements, a first electrode for expanding or contracting a first region of the piezoelectric elements in the group of piezoelectric elements and a second electrode for expanding or contracting a second region of the piezoelectric elements in the group of piezoelectric elements are disposed along the axial direction, wherein in each group of piezoelectric elements, a common third electrode or a separate third electrode paired with the first electrode and the second electrode is disposed such that the vibration element of the piezoelectric actuator has: a bending mode in which a middle portion in the axial direction becomes convex or concave, so that end portions of the vibration element move in the axial direction at both ends in the axial direction; an expansion/contraction pattern in which one end portion at both ends of the axial direction expands/contracts with time and the other end portion expands/contracts with opposite phases, whereby the end portion of the vibration element moves in a direction perpendicular to the axial direction, wherein the controller is configured to make the end portion of the vibration element perform an elliptical motion, which is a combination of a vibration component in the axial direction and a vibration component perpendicular to the axial direction, by applying the same frequency oscillating voltage signal to the first electrode and the second electrode, wherein the controller is configured to control a vibration amplitude of the vibration component in the axial direction and a vibration amplitude of the vibration component perpendicular to the axial direction by controlling a phase difference between the voltage signal applied to the first electrode and the voltage signal applied to the second electrode, wherein vibration of a first mode based on the bending mode is generated in the vibration element when the oscillating voltage signals applied to the first electrode and the second electrode are in phase; when the oscillating voltage signals applied to the first electrode and the second electrode are in opposite phases, vibration of a second mode based on the expansion/contraction mode is generated in the vibration element.

According to a first implementation form of the third aspect of the application, a driving device for driving a driven element is provided. The driving apparatus includes: a piezoelectric actuator including a vibration element in contact with a driven element and one or more sets of piezoelectric elements attached to the vibration element; a controller for controlling a voltage signal applied to the piezoelectric element to vibrate the vibration element of the piezoelectric actuator to drive the driven element; a voltage boosting circuit for converting a voltage of a power source into a voltage for driving the piezoelectric actuator, wherein the voltage boosting circuit includes a driver for supplying a voltage to the piezoelectric actuator through an external inductor, the piezoelectric actuator is represented by an equivalent circuit including an internal R-L-C (resistor-inductor-capacitor) series resonant circuit and a capacitance component connected in parallel, a resonance frequency of an R-L-C series resonant circuit composed of an output impedance of the driver, the external inductor, and the capacitance component of the piezoelectric actuator substantially matches a resonance frequency of the internal R-L-C series resonant circuit of the piezoelectric actuator, wherein (i) a parameter of the internal R-L-C series resonant circuit of the piezoelectric actuator is adjusted, and/or (ii) the voltage boosting circuit has an external capacitor connected in parallel with the capacitance component of the piezoelectric actuator such that an inductance of the external inductor is 30 μh or less.

According to this implementation, the piezoelectric actuator can be driven even when the power supply voltage (e.g., the power supply voltage of the portable device) is lower than the voltage required to drive the piezoelectric actuator. Furthermore, the size of the external inductor is relatively small, which makes the external inductor suitable for inclusion into a portable device. Furthermore, small inductances can be achieved by changing the circuit parameter design within the piezoelectric actuator and/or adding external elements.

According to a second implementation of the third aspect of the present application, which is based on the first implementation of the third aspect of the present application, each group of piezoelectric elements comprises one or more piezoelectric elements, in each group of piezoelectric elements, a first electrode for expanding or contracting a first region of the piezoelectric elements of the group of piezoelectric elements and a second electrode for expanding or contracting a second region of the piezoelectric elements of the group of piezoelectric elements are arranged along the axial direction, wherein in each group of piezoelectric elements a common third electrode or a separate third electrode paired with the first electrode and the second electrode is arranged such that the vibrating element of the piezoelectric actuator has: a bending mode in which a middle portion in the axial direction becomes convex or concave, so that end portions of the vibration element move in the axial direction at both ends in the axial direction; an expansion/contraction mode in which one end portion at both ends of the axial direction expands/contracts and the other end portion expands/contracts with time in opposite phases, whereby the end portion of the vibration element moves in a direction perpendicular to the axial direction, wherein the controller is configured to vibrate the vibration element by applying an oscillating voltage signal of the same frequency to the first electrode and the second electrode, thereby driving the driven element in contact with the vibration element in the axial direction, wherein vibration of a first mode based on the bending mode is generated in the vibration element when the oscillating voltage signals applied to the first electrode and the second electrode are in phase; when the oscillating voltage signals applied to the first electrode and the second electrode are in opposite phases, a vibration of a second mode based on the expansion/contraction mode is generated in the vibration element, wherein the controller is configured to control a speed of the driven element by controlling a phase difference between the voltage signal applied to the first electrode and the voltage signal applied to the second electrode.

According to a third implementation form of the third aspect as such or as based on the second implementation form of the third aspect of the application, the voltage signal is applied to the first electrode and the second electrode to cause the end portion of the vibrating element to perform an elliptical motion, the elliptical motion being a combination of a vibration component in the axial direction and a vibration component perpendicular to the axial direction, and the controller is configured to control a vibration amplitude of the vibration component in the axial direction and a vibration amplitude of the vibration component perpendicular to the axial direction by controlling the phase difference.

According to a fourth aspect of the present application, there is provided an electronic device comprising a driving device according to any one of the implementations of the first to third aspects of the present application.

According to a fifth aspect of the present application, there is provided an electronic device comprising a camera, wherein the camera comprises a driving device according to any one of the first to third aspects of the present application, wherein the driving device is configured to drive a lens unit of the camera attached to the driven element for auto-focusing.

According to a sixth aspect of the present application, there is provided an electronic device according to the fourth or fifth aspect, the electronic device being a cell phone or a smart phone.

According to a first implementation of the seventh aspect of the present application, a method of controlling a piezoelectric actuator by a driver to drive a driven element in an axial direction is provided. The piezoelectric actuator includes: a vibrating element in contact with the driven element and one or more sets of piezoelectric elements attached to the vibrating element; wherein each group of piezoelectric elements includes one or more piezoelectric elements in which a first electrode for expanding or contracting a first region of the piezoelectric elements in the group of piezoelectric elements and a second electrode for expanding or contracting a second region of the piezoelectric elements in the group of piezoelectric elements are disposed along the axial direction, wherein in each group of piezoelectric elements a common third electrode or a separate third electrode paired with the first electrode and the second electrode is disposed such that the vibration element of the piezoelectric actuator has: a bending mode in which a middle portion in the axial direction becomes convex or concave, so that end portions of the vibration element move in the axial direction at both ends in the axial direction; an expansion/contraction mode in which one end portion expands/contracts at both ends of the axial direction and the other end portion expands/contracts with time in opposite phases, whereby the end portion of the vibration element moves in a direction perpendicular to the axial direction, wherein the method includes: vibrating the vibration element by applying an oscillating voltage signal of the same frequency to the first electrode and the second electrode, thereby driving the driven element in contact with the vibration element in the axial direction, controlling a speed of the driven element by controlling a phase difference between the voltage signal applied to the first electrode and the voltage signal applied to the second electrode, wherein when the oscillating voltage signals applied to the first electrode and the second electrode are in phase, vibration of a first mode based on the bending mode is generated in the vibration element; when the oscillating voltage signals applied to the first electrode and the second electrode are in opposite phases, vibration of a second mode based on the expansion/contraction mode is generated in the vibration element.

According to a second implementation of the seventh aspect of the present application based on the first implementation of the seventh aspect of the present application, applying the voltage signal to the first electrode and the second electrode causes the end portion of the vibration element to perform an elliptical motion, the elliptical motion being a combination of a vibration component in the axial direction and a vibration component perpendicular to the axial direction, and controlling the speed of the driven element by controlling the phase difference includes controlling the vibration amplitude of the vibration component in the axial direction and the vibration amplitude of the vibration component perpendicular to the axial direction by controlling the phase difference.

The advantages achieved by the dependent implementations of the first implementation manner based on the seventh aspect are the same as or similar to the corresponding implementation manner of the first aspect, and are not described here again.

According to a third implementation of the seventh aspect of the present application based on the first or second implementation of the seventh aspect of the present application, the method further comprises making the phase difference substantially pi so that the speed of the driven element is zero.

According to a fourth implementation form of the seventh aspect of the application as such or based on the first or second implementation form of the seventh aspect of the application, the method further comprises: the phase difference is gradually reduced or increased from substantially pi when driving the driven element from zero speed is started, and/or gradually approximated to approximately pi when the speed of the driven element is set to zero.

According to a fifth implementation form of the seventh aspect as such or as based on any of the first to third implementation forms of the seventh aspect, the method further comprises controlling the amplitude of the voltage signals applied to the first and second electrodes to compensate for amplitude variations of the vibration component perpendicular to the axial direction caused by the control of the phase difference.

According to a sixth implementation of the seventh aspect of the present application based on any of the first to fifth implementation of the seventh aspect of the present application, the method further comprises controlling the speed of the driven element by further controlling the frequency and/or amplitude of the voltage signal applied to the first and second electrodes.

According to a seventh implementation form of the seventh aspect as such or as based on any of the first to fifth implementation forms of the seventh aspect, the method further comprises controlling the speed of the driven element by controlling the frequency and/or amplitude of the voltage signal applied to the first and second electrodes, instead of the phase of the voltage signal, when the speed of the driven element is equal to or greater than a predetermined value.

According to an eighth aspect of the present application, there is provided a computer program for causing a driver to execute the method according to any one of the first to seventh implementations of the seventh aspect of the present application.

According to a ninth aspect of the present application, there is provided a computer readable storage medium having stored thereon a computer program according to the eighth aspect of the present application.

Drawings

FIG. 1 illustrates a schematic diagram of driving a driven element in an axial direction by a piezoelectric actuator controlled by a controller in accordance with an embodiment of the present application;

FIG. 2 illustrates a piezoelectric actuator according to an embodiment of the present application;

FIG. 3 illustrates the principle of a piezoelectric actuator according to an embodiment of the present application;

FIG. 4 illustrates elliptical motion in a piezoelectric actuator according to an embodiment of the present application;

FIG. 5 illustrates two-phase signals applied to a piezoelectric actuator in accordance with an embodiment of the present application;

Fig. 6 shows a relationship between a phase difference in elliptical motion and a thrust in a piezoelectric actuator according to an embodiment of the present application;

FIG. 7 is a flow chart of a method for driving a piezoelectric actuator in an axial direction to control movement of a driven element according to an embodiment of the present application;

fig. 8 shows parameters of an equivalent circuit of a piezoelectric actuator and a booster circuit according to an embodiment of the present application;

fig. 9 shows parameters of an equivalent circuit of a piezoelectric actuator and a booster circuit according to an embodiment of the present application;

Fig. 10 shows an electronic device comprising a driving device comprising a piezoelectric actuator according to an embodiment of the application.

Detailed Description

Although embodiments of the present application are described below with reference to the accompanying drawings, the present application is not limited to the embodiments shown or described.

Piezoelectric actuators (also known as piezoelectric actuators (piezoelectric actuator)) despite their small size, offer high energy density and high power, and have long been used in single lens reflex cameras and other applications. Since a device using a piezoelectric actuator to drive a driven element may be referred to as a piezoelectric motor, the terms piezoelectric actuator and piezoelectric motor may be used synonymously. A piezoelectric motor that linearly drives a driven element along an axis by vibration of the piezoelectric element in an ultrasonic range may be referred to as a linear ultrasonic motor (USM).

Fig. 1 shows a schematic diagram of driving a driven element 120 in an axial direction by a piezoelectric actuator 100 controlled by a controller 110 according to an embodiment of the present application. A controller, as used herein, generally refers to one or more components, including circuitry for applying voltage signals (also referred to as drive signals) to operate a piezoelectric actuator and circuitry for controlling the voltage. The control of the voltage signal may be performed according to a computer program stored on a storage medium.

Fig. 2 (a) shows a piezoelectric actuator 200 for driving a driven element in an axial direction according to an embodiment of the present application. According to the present embodiment, one or more sets of piezoelectric elements 220 are attached around a vibrating element (vibrator) 210. As described below, in the example shown, the vibrating element has a hole into which the cylindrical driven element is inserted. However, the shape of the vibration element is not limited to the illustrated example. As described below, in the example shown, each set of piezoelectric elements includes a piezoelectric element 220 having electrodes 230 and 240. However, each set of piezoelectric elements may include a piezoelectric element having electrode 230 and a separate piezoelectric element having electrode 240. The piezoelectric elements of each set of piezoelectric elements include a first electrode 230 for expanding or contracting a first region of the piezoelectric elements of the set of piezoelectric elements and a second electrode 240 for expanding or contracting a second region of the piezoelectric elements of the set of piezoelectric elements. The first electrode 230 and the second electrode 240 are disposed in the axial direction. In the illustrated example, each group of piezoelectric elements includes one piezoelectric element 220, and the first region and the second region are two regions of the same piezoelectric element 220, but the present application is not limited thereto. For example, the piezoelectric elements in each set of piezoelectric elements may include two piezoelectric elements, and the first region and the second region may belong to separate piezoelectric elements. By the controlled vibration of the vibration element 210, the cylindrical driven element 250 inserted into the hole of the vibration element is driven in the axial direction. The first region and the second region of the piezoelectric element are disposed along the axial direction of the insertion hole. One or more electrodes paired with the first electrode and the second electrode are connected to Ground (GND), as described below in connection with (b) in fig. 2.

The invention is not limited to the embodiments shown. These piezoelectric elements may be attached at symmetrical positions around the vibrating element. The shape of the vibration element is not limited, and particularly, is not limited to a shape having a hole into which a columnar driven element is inserted, as long as the vibration element is in contact with the driven element and applies a force to the driven element. The piezoelectric element may be, but is not limited to, a PZT (lead zirconate titanate) element. Further, although piezoelectric elements are used herein as examples, any suitable electromechanical transducer may be used. Furthermore, although the description herein uses an actuator or the like that drives a driven element, it will be apparent to the skilled person that this is a description from the perspective of the actuator (or some component that holds the actuator), typically causing relative movement between the actuator and the driven element. The vibrating element may be referred to as a stator. The driven element may be referred to as a slider, a shaft, or the like. The use of such terms does not limit which of the actuator or driven element is stationary. Further, more than one piezoelectric actuator as shown in the figures may be provided along the axial direction of the driven element.

Fig. 2 (b) shows a driving voltage applied to the piezoelectric actuator shown in fig. 2 (a). The first voltage signal Ea is applied to the first electrode 230, and the second voltage signal Eb is applied to the second electrode 240. These voltage signals may be two-phase voltage signals, which in one embodiment may be defined as:

Ea ＝ a * sin ωt (1)

Eb ＝ a * sin (ωt + ps) (2)

Where a is the signal amplitude, ps is the phase difference between Ea and Eb, ω is the angular frequency, and t is the time. The signal amplitudes and angular frequencies of the first voltage signal and the second voltage signal are the same.

In one embodiment, the vibrating element is made of a conductor such as metal. In fig. 2 (b), GND represents ground. In one embodiment, a third electrode paired with the first electrode is present on the opposite side of the piezoelectric element from the first electrode, and the first voltage signal Ea is applied between the first electrode and the third electrode. The third electrode may be placed between the piezoelectric element and the vibration element made of a conductor. Similarly, a fourth electrode paired with the second electrode is present on the opposite side of the piezoelectric element from the second electrode, and a second voltage signal Eb is applied between the second electrode and the fourth electrode. The fourth electrode may be placed between the piezoelectric element and the vibration element made of a conductor. The third electrode and the fourth electrode may be separate electrodes or may be a common electrode. The third and fourth electrodes are connected to Ground (GND) to provide a reference for the voltage signal. In the embodiment shown in fig. 2 (b), the vibration element is made of a conductor, and the conductor is connected to Ground (GND).

Fig. 3 is a schematic view of a cross section of the piezoelectric actuator shown in fig. 2 for explaining the principle of the piezoelectric actuator of the present application.

Fig. 3 (a) shows the vibration of the vibration element when ps=0 (i.e., when Ea and Eb are in phase) (this is referred to as a bending mode). As the middle portion vibrates up and down, the end portions (e.g., points represented by open circles) move laterally. Accordingly, the bending mode generates axial vibration at the end of the vibration element. This generates an axial thrust as described below.

Fig. 3 (b) shows the vibration of the vibration element when ps=pi (i.e., when Ea and Eb are in opposite phases). This is a vibration mode in which one end expands/contracts and the other end expands/contracts in the opposite phase, and is called an expansion/contraction vibration mode or an expansion/contraction mode. When the wall of the vibrating element is inclined, the end (for example, a point indicated by an open circle) moves up and down. Accordingly, the expansion/contraction mode generates vibration in a direction perpendicular to the axis (in a direction perpendicular to the plane of the piezoelectric element).

For the general phase ps, the end of the vibration element performs a motion consisting of axial vibration and up-down direction (direction perpendicular to the axis) vibration. The magnitude of the axial vibration may be considered to be proportional to ea+eb (this may be referred to as the first mode, similar to the bending mode described above). The magnitude of the vibration in the direction perpendicular to the axis may be considered to be proportional to Ea-Eb (this may be referred to as the second mode, similar to the expansion/contraction mode described above). It should be noted that this does not illustrate that the addition or subtraction of Ea and Eb applied to different electrodes is performed as an electrical signal. Vibrations caused by these voltages are combined together at the ends of the vibrating element.

The vibration amplitude of the vibration component in the axial direction and the vibration amplitude of the vibration component in the direction perpendicular to the axis, which are caused by the piezoelectric actuator at the end of the vibration element, can be estimated to be proportional to equation (3) and equation (4), respectively, as follows:

(in-phase) ea+eb=a (sin (ωt+ps) +sin ωt) =2×acos (ps/2) ×sin (ωt+ps/2) (3)

(Opposite phase) Ea-eb=a (sin (ωt+ps) -sin ωt) =2×a sin (ps/2) ×cos (ωt+ps/2) (4)

In the embodiment of the present application, the phase difference ps between the voltage signals Ea and Eb applied to the first electrode and the second electrode of the piezoelectric actuator is set equal to pi/2. (it should be noted that the value of ps may be controlled by a controller, as described below.) in this case, as shown in (c) of fig. 3, the end portion of the vibrating element (for example, a point indicated by an open circle) makes an elliptical motion. Such elliptical motion axially translates (pushes, drives or advances) the driven element inserted into the bore of the vibratory element.

Fig. 4 shows an elliptical motion, which is caused by the vibration of the vibration element at the end of the vibration element, and is a combination of the vibration amplitude of the vibration component in the axial direction (thrust direction, translational motion direction of the driven element) and the vibration amplitude of the vibration component in the direction perpendicular to the axis. The direction of movement of the driven element is also shown.

Fig. 5 shows an example of a two-phase signal in the case of ps=pi/2, which causes elliptical motion as shown in (c) in fig. 3. At time a, when the two curves of these voltage signals intersect, ea and Eb have the same sign and the same magnitude, which corresponds to the case of (i) in fig. 3 (c). Thereafter, when the two signals are the same in size and opposite in sign, time B corresponds to (ii) in (c) in fig. 3. At time C, when the two curves intersect again, ea and Eb again have the same sign and the same size, which corresponds to (iii) in (C) of fig. 3. When the two signals are the same in size and opposite in sign, time D corresponds to (iv) in (D) of fig. 3.

It should be noted that although the voltage signals Ea and Eb are represented here as sine waves for ease of understanding, it may be advantageous to use other waveforms such as square waves, triangular waves, saw tooth waves, etc. For example, waveforms that facilitate digital control of the voltage signals applied to the first and second electrodes may be employed.

The vibrating element needs to press the driven element downwards with a relatively large force so that the driven element can be driven by the piezoelectric actuator. In the conventional piezoelectric motor, when driving the driven element is started, a relatively large force is required to overcome static friction generated when the driven element is in a stationary state with respect to the vibration element. At the moment the driven element starts to move, the static friction becomes dynamic friction, resulting in a sudden decrease in friction. This is problematic because the driven element suddenly begins to move. On the other hand, when the speed of the driven member is reduced, the dynamic friction becomes static friction, which causes a sudden increase in friction force, which may cause the driven member to suddenly stop. By controlling the frequency or amplitude of the voltage signal used to drive the piezoelectric actuator, low speed control is difficult because low speed control requires precise control of the voltage or feed forward control (e.g., applying more force to overcome stiction only at the beginning of movement).

The present inventors have recognized from equations (3) and (4) set forth above that in elliptical motion of the end portion of the vibration element that drives the driven element, the ratio of the amplitude of the component in the axial direction and the amplitude of the component perpendicular to the axial direction can be controlled by changing the value of ps, and the overall amplitude can be changed by changing the value of a.

Fig. 6 shows the relationship between the vibration amplitude in the axial direction (horizontal axis) and the vibration amplitude perpendicular to the axial direction (vertical axis) in the case of the phase differences ps=pi/2, (3/4) pi, (11/12) pi, and pi. The case of ps=pi/2 has the highest efficiency of thrust generation. In the case of the phase difference p= (3/4) pi, the force pressing the driven element is large, and the thrust force is small. In the case of the phase difference ps=pi, the thrust is zero.

Thus, by varying the value of ps rather than controlling the frequency or amplitude of the voltage signal applied to the piezoelectric actuator, the controller of the driving apparatus can control the thrust on the driven element without being affected by switching between static friction and dynamic friction. At the beginning of the movement, the thrust can be gradually increased from zero by gradually decreasing the value of ps from pi. In the case of ps=pi/2, the efficiency of thrust generation is highest. Or the thrust force may be gradually increased from zero in the opposite direction by gradually increasing the value of ps from pi. In the case of ps= (3/2) pi, the efficiency of generating the opposite thrust is highest. When stopped, the thrust force can be gradually made zero by gradually bringing the value of ps close to pi. Even when ps=pi and there is no thrust, the vibration element vibrates in a direction perpendicular to the thrust. Thus, the friction between the vibrating element and the driven element is dynamic friction. This can avoid problematic behavior in that when starting to move the driven element, switching from stiction to dynamic friction causes the driven element to suddenly start moving, or the driven element suddenly stops due to switching from dynamic friction to stiction. Thus, the movement improves the linearity of the movement with respect to the control signal.

Therefore, the method of controlling a piezoelectric actuator according to the present application can improve low-speed control because changing the phase difference can freely control the thrust on the driven element without being affected by the switching between static friction and dynamic friction.

According to embodiments of the present application, in addition to or as an alternative to controlling the phase difference between the voltage signals applied to the first and second electrodes, the frequency and/or amplitude of the voltage signals applied to the first and second electrodes may be controlled.

As can be seen from the equations (3) and (4) set forth above, when the amplitude a of the voltage signal is kept unchanged, since the thrust force generated by the vibration component in the axial direction of the elliptical motion is reduced by changing the phase difference ps from pi/2 to pi, the vibration amplitude in the direction perpendicular to the axis increases. According to the embodiment of the present application, when the phase difference ps is changed, the signal amplitude a may also be changed to compensate for such an increase in the vibration amplitude in the direction perpendicular to the axis.

Fig. 7 is a flowchart showing an outline of a method of driving the piezoelectric actuator in a case where the driven element in a stationary state moves in the axial direction and is stationary again. In one embodiment, the driving may be performed by the controller 110 of fig. 1. In one embodiment, the desired speed of the driven element in the axial direction is provided by a high-level controller or user. In a non-limiting embodiment for driving a lens unit for auto-focusing in moving picture imaging, the desired speed is a speed for moving the lens unit to move the lens unit to a desired position for focusing, which may be dynamically determined by a high-level controller. It should be noted that the term "controller 110" or "higher-level controller" refers to a logical distinction. The controller 110 and the higher-level controller may be physically implemented by the same controller. The embodiments are not limited thereto.

In one embodiment, the high level controller determines a non-zero speed indication value based on the current position and the desired position of the driven element (e.g., lens unit). When the driven element reaches the desired position, the speed indication value is determined to be zero. In one embodiment, the higher level controller may gradually increase the speed indication value from zero and gradually decrease it to zero so that the driven element smoothly starts moving and then smoothly stops. In one embodiment, a position sensor for detecting the position of the driven element is provided that lets the high-level controller know the position of the driven element. In one embodiment, the position of the driven element is periodically detected and the speed of the driven element may be determined based on a difference from a previously detected value. Thus, it can be determined whether the desired speed is reached.

Referring to the flowchart of fig. 7, at step 710, the driven element is stationary and the voltage signals applied to the first and second electrodes of the piezoelectric element of the piezoelectric actuator are disconnected.

At step 720, the controller 110 receives a speed indicator value (instead of zero) for the driven element from the higher level controller.

At step 730, the controller 110 begins to apply an oscillating voltage signal of the same frequency across the first and second electrodes of the piezoelectric actuator. Initially, the phase difference between the voltage signals applied to the first electrode and the second electrode is substantially pi. In this case, the end portion of the vibration element of the piezoelectric actuator vibrates only in the direction perpendicular to the axis, and does not drive the driven element in the axial direction. Since power is lost without the driven element moving, it is desirable to begin applying voltage signals to the first and second electrodes after receiving a speed indication value (rather than zero) of the driven element, although the application is not so limited.

In step 740, the controller 110 sets a phase difference between the voltage signals applied to the first electrode and the second electrode to be in the range of pi to (3/2) pi or pi to pi/2 according to the received speed indication value. The direction in which the driven element moves (e.g., positive direction) when the phase difference is in the range of pi to (3/2) pi is opposite to the direction in which the driven element moves (e.g., negative direction) when the phase difference is in the range of pi to pi/2. In one embodiment, the controller 110 may set the phase difference according to a lookup table (LUT) indicating a correspondence between a desired speed indication value and the phase difference, although the present application is not limited thereto.

The controller 110 dynamically adjusts the phase difference between the voltage signals applied to the first electrode and the second electrode according to the speed indication value received from the higher-level controller. The phase difference of pi/2 (or (3/2) pi) corresponds to this most efficient driving of thrust by phase difference control. It should be noted that, in order to obtain a greater speed, the controller 110 may control the amplitude and frequency of the voltage signals applied to the first and second signals in addition to the phase difference between the voltage signals applied to the first and second electrodes.

At step 750, the controller 110 receives a speed indication value of zero from the higher level controller. This may occur, for example, when the driven element reaches a desired position. It should be noted that in some embodiments, the higher level controller may take into account the inertia of the driven element and determine the speed indication value as zero before the driven element reaches the desired position.

In step 760, the controller 110 sets a phase difference between the voltage signals applied to the first electrode and the second electrode to be substantially equal to pi. Also, the end portion of the vibration element of the piezoelectric actuator vibrates only in the direction perpendicular to the axis, and does not move the driven element in the axial direction.

At step 770, the controller 110 turns off the voltage signals applied to the first electrode and the second electrode. This eliminates power loss when the driven element is not moving.

Step 780 is the final state in which the driven element is stationary and the voltage signals applied to the first and second electrodes are off.

It should be noted that when the speed of the driven element is equal to or greater than the predetermined value, the speed of the driven element may be controlled by controlling the frequency and/or amplitude of the voltage signals applied to the first electrode and the second electrode, instead of controlling the phase difference between the voltage signals applied to the first electrode and the second electrode. In high speed conditions, control by frequency and/or amplitude may be effective because there is no problem due to switching between static friction and dynamic friction, which may lead to abrupt start of movement or abrupt stop.

Another aspect of the present invention relates to a voltage boosting device or a voltage boosting circuit (device or circuit for boosting voltage) for supplying a driving voltage to a piezoelectric actuator.

Since the piezoelectric actuator requires a high voltage (for example, 40V to 100V), in order to integrate the piezoelectric actuator in a portable device such as a smart phone (typically, operating at a voltage of about 3V), a step-up device (a device for increasing the voltage) is required. The piezoelectric actuator mentioned in this aspect of the invention may be, but is not limited to, the piezoelectric actuator described with reference to fig. 2 to 7 above.

The piezoelectric actuator may be represented by an equivalent circuit comprising an internal R-L-C (resistor-inductor-capacitor) series resonant circuit and a capacitive component Cd connected in parallel. In fig. 8, the equivalent circuit corresponds to a portion surrounded by a broken line.

In one embodiment, the boost circuit includes a driver for providing a voltage to the piezoelectric actuator through an external inductor. The output voltage Vout and resonant frequency f ₀ out of the boost circuit can be expressed as

Where Vin is the input voltage from the power supply, rout is the internal resistance of the driver, lext is the inductance of the external inductor, and Cd is the capacitive component of the piezoelectric actuator.

The resonant frequency of the R-L-C (resistor-inductor-capacitor) series resonant circuit, which is determined by the output impedance Rout of the driver, the inductance Lext of the external inductor, and the capacitance component Cd of the piezoelectric actuator (referred to herein as the driver-side resonant frequency), substantially matches the resonant frequency of the internal R-L-C series resonant circuit of the piezoelectric actuator. This matching can maximize the drive amplitude. Strictly speaking, the driver side resonant frequency also relates to the contribution from the internal R-L-C series resonant circuit of the piezoelectric actuator, but this contribution is negligible because the output impedance Rout of the driver is much smaller than the resistance R (R > > Rout) of the internal R-L-C series resonant circuit of the piezoelectric actuator. As a non-limiting example, rout represents 1 ohm and R represents 5 kiloohms.

However, components inside portable electronic devices such as smartphones are very small. When the inductance Lext of the external inductor is several tens of muh, the component height may exceed 1mm, which makes the external inductor unsuitable for inclusion into a portable electronic device. Therefore Lext should be as small as possible.

Generally, various types of inductors are known, including coil inductors having coiled wires, stacked inductors having a stack of sheets with conductive traces printed thereon, and thin film inductors patterned with coil-shaped metal films by sputtering or vapor deposition as is known using semiconductor fabrication techniques. The laminated inductor and the thin film inductor are generally smaller than the coil inductor and thus are suitable for being mounted in a portable device such as a smart phone, but the inductance of the laminated inductor and the thin film inductor is generally smaller than the coil inductor.

The present application proposes two ways to reduce the inductance of the external inductor Lext. Embodiments of the application based on these approaches enable the use of inductors with smaller inductances, which enable the use of stacked inductors or thin film inductors as external inductors.

According to a first approach, the desired or allowed value Lext is first determined according to the requirements of the component height. Based on the determined Lext value, the resonant frequency of the piezoelectric actuator is designed so as to satisfy the above-described resonance condition. For example, the parameters of the R-L-C series resonant circuit in the piezoelectric actuator are adjusted such that the inductance of the external inductor is less than 30 μh (or preferably less than 20 μh or most preferably less than 10 μh). This is in contrast to conventional design techniques in which the parameters of the motor are fixed and the value of Lext is determined accordingly. It should be noted, however, that current designs typically result in higher resonant frequencies, which tend to increase switching losses.

In the second way, as shown in fig. 9, by adding an external capacitor having a capacitance Cadd in parallel with the capacitance component Cd of the piezoelectric actuator, the two resonance frequencies are substantially matched. The output voltage Vout and resonant frequency f ₀ out of the boost circuit can be expressed as

Where Cadd is the capacitance of the additional parallel capacitor. Other parameters are defined as above.

The addition of such a parallel capacitor increases the output current of the driver due to the additional current flowing through the additional capacitor, but does not waste energy, since such a parallel capacitor is reactive power which consumes no energy. Larger output currents require an increase in the size of the driver element, but such increases in size are generally within the range that can be tolerated in typical implementations (e.g., smartphones).

This exemplary embodiment of this aspect of the present invention can reduce the inductance of the external inductor of the driver in the step-up device for supplying the driving voltage to the piezoelectric actuator. This facilitates the inclusion of a boost circuit in a small portable electronic device.

Fig. 10 illustrates a portable electronic device, such as a smart phone, incorporating any of the embodiments of any of the aspects of the present application. The embodiment of the application can be used for automatic focusing of portable electronic equipment such as smart phones and the like, but the use of the embodiment of the application is not limited to the automatic focusing.

Although various embodiments are described above and shown in the drawings, the invention is not limited to the specific embodiments described or shown.

The unit division disclosed in the embodiments of the present application is not limited, and other component divisions may be configured in the embodiments.

Where appropriate, some of the functions may be implemented in the form of a computer program for causing a processor or computing device to perform one or more functions. For example, various signal processing and control functions may be implemented as computer programs. The computer program may be stored on a non-transitory computer readable storage medium. The storage medium may be any medium that can store a computer program, and may be: solid state memory, e.g., USB drive, flash drive, read-only memory (ROM), random-access memory (RAM); magnetic storage media such as removable or non-removable hard disks; or an optical storage medium such as an optical disc.

The above description is only illustrative of various embodiments of the application and is not intended to limit the scope of the application. Any variations which would be apparent to a person skilled in the art in light of the present disclosure would fall within the scope of the present disclosure. For example, individually disclosed measures may be combined appropriately in a single embodiment as long as the measures are not mutually exclusive.

Claims

1. A driving apparatus for driving a driven element in an axial direction, the driving apparatus comprising:

a piezoelectric actuator, wherein the piezoelectric actuator includes a vibration element in contact with a driven element and one or more groups of piezoelectric elements attached to the vibration element;

The controller is used for controlling the operation of the controller,

Wherein each group of piezoelectric elements includes one or more piezoelectric elements in which a first electrode for expanding or contracting a first region of the piezoelectric elements in the group of piezoelectric elements and a second electrode for expanding or contracting a second region of the piezoelectric elements in the group of piezoelectric elements are disposed along the axial direction, wherein in each group of piezoelectric elements a common third electrode or a separate third electrode paired with the first electrode and the second electrode is disposed such that the vibration element of the piezoelectric actuator has:

A bending mode in which a middle portion in the axial direction becomes convex or concave, so that end portions of the vibration element move in the axial direction at both ends in the axial direction;

An expansion/contraction mode in which one end portion at both ends of the axial direction expands/contracts and the other end portion expands/contracts with time in opposite phases, whereby the end portion of the vibration element moves in a direction perpendicular to the axial direction,

Wherein the controller is configured to vibrate the vibration element by applying an oscillating voltage signal of the same frequency to the first electrode and the second electrode, thereby driving the driven element in contact with the vibration element in the axial direction,

Wherein when the oscillating voltage signals applied to the first electrode and the second electrode are in phase, vibrations of a first mode based on the bending mode are generated in the vibration element; when the oscillating voltage signals applied to the first electrode and the second electrode are in opposite phases, vibrations of a second mode based on the expansion/contraction mode are generated in the vibration element,

Wherein the controller is configured to control a speed of the driven element by controlling a phase difference between the voltage signal applied to the first electrode and the voltage signal applied to the second electrode.

2. The driving apparatus as recited in claim 1, wherein said voltage signal is applied to said first electrode and said second electrode to cause said end portion of said vibration element to perform an elliptical motion which is a combination of a vibration component in said axial direction and a vibration component perpendicular to said axial direction,

The controller is configured to control a vibration amplitude of the vibration component in the axial direction and a vibration amplitude of the vibration component perpendicular to the axial direction by controlling the phase difference.

3. A driving apparatus as claimed in claim 1 or 2, wherein the vibrating element comprises a bore, the driven element comprises a cylindrical shape, and the driven element inserted into the bore is driven in the axial direction.

4. A driving apparatus as claimed in any one of claims 1 to 3, wherein the one or more sets of piezoelectric elements attached to the vibration element include two or more sets of piezoelectric elements attached in symmetrical positions with respect to the vibration element, a first identical voltage signal being applied to the first electrode of each piezoelectric element, and a second identical voltage signal being applied to the second electrode of each piezoelectric element.

5. A driving apparatus as claimed in any one of claims 1 to 4, wherein the controller is arranged to cause the phase difference to be substantially pi so that the speed of the driven element is zero.

6. The driving apparatus as claimed in any one of claims 1 to 5, wherein,

The controller is used for gradually reducing or increasing the phase difference from substantially pi when the driven element starts to be driven from zero speed, and/or

The controller is configured to gradually approach the phase difference to approximately pi when the speed of the driven element is set to zero.

7. The drive apparatus according to claim 2, wherein the controller is further configured to control an amplitude of the voltage signal applied to the first electrode and the second electrode to compensate for a variation in amplitude of the vibration component perpendicular to the axial direction caused by the control of the phase difference.

8. A driving device according to any one of claims 1 to 7, wherein the controller is adapted to control the speed of the driven element by further controlling the frequency and/or amplitude of the voltage signals applied to the first and second electrodes.

9. A driving apparatus as claimed in any one of claims 1 to 7, wherein the controller is adapted to control the speed of the driven element by controlling the frequency and/or amplitude of the voltage signal applied to the first and second electrodes, but not the phase of the voltage signal, when the speed of the driven element is equal to or greater than a predetermined value.

10. The drive device according to any one of claims 1 to 9, wherein the voltage signal applied to the first electrode and the second electrode is a square wave, a triangular wave, a sawtooth wave, or a sine wave.

11. The driving apparatus according to any one of claims 1 to 10, further comprising a booster circuit, wherein the booster circuit is configured to convert a voltage of a power source into a voltage for driving the piezoelectric actuator.

12. The drive apparatus of claim 11, wherein the boost circuit includes a driver for providing a voltage to the piezoelectric actuator through an external inductor.

13. The driving apparatus as claimed in claim 12, wherein the piezoelectric actuator is represented by an equivalent circuit including an internal R-L-C (resistor-inductor-capacitor) series resonant circuit and a capacitance component connected in parallel,

The resonant frequency of an R-L-C series resonant circuit comprised of the output impedance of the driver, the external inductor, and the capacitive component of the piezoelectric actuator substantially matches the resonant frequency of the internal R-L-C series resonant circuit of the piezoelectric actuator.

14. The drive apparatus according to claim 13, wherein parameters of the internal R-L-C series resonant circuit of the piezoelectric actuator are adjusted so that an inductance of the external inductor is 30 μh or less.

15. The drive apparatus according to claim 13, wherein the step-up circuit has an external capacitor connected in parallel with the capacitance component of the piezoelectric actuator such that an inductance of the external inductor is 30 μh or less.

16. A driving apparatus, characterized in that the driving apparatus comprises:

A piezoelectric actuator including a vibration element and one or more sets of piezoelectric elements attached to the vibration element;

The controller is used for controlling the operation of the controller,

Wherein the controller is configured to make the end portion of the vibration element perform an elliptical motion, which is a combination of a vibration component in the axial direction and a vibration component perpendicular to the axial direction, by applying the oscillation voltage signal of the same frequency to the first electrode and the second electrode,

Wherein the controller is configured to control a vibration amplitude of the vibration component in the axial direction and a vibration amplitude of the vibration component perpendicular to the axial direction by controlling a phase difference between the voltage signal applied to the first electrode and the voltage signal applied to the second electrode,

Wherein when the oscillating voltage signals applied to the first electrode and the second electrode are in phase, vibrations of a first mode based on the bending mode are generated in the vibration element; when the oscillating voltage signals applied to the first electrode and the second electrode are in opposite phases, vibration of a second mode based on the expansion/contraction mode is generated in the vibration element.

17. A driving apparatus for driving a driven element, the driving apparatus comprising:

A piezoelectric actuator including a vibration element in contact with a driven element and one or more sets of piezoelectric elements attached to the vibration element;

A controller for controlling a voltage signal applied to the piezoelectric element to vibrate the vibration element of the piezoelectric actuator to drive the driven element;

A voltage boosting circuit for converting a voltage of a power source into a voltage for driving the piezoelectric actuator,

Wherein the boost circuit includes a driver for providing a voltage to the piezoelectric actuator through an external inductor,

The piezoelectric actuator is represented by an equivalent circuit comprising an internal R-L-C (resistor-inductor-capacitor) series resonant circuit and a capacitive component connected in parallel,

The resonant frequency of the R-L-C series resonant circuit comprised of the output impedance of the driver, the external inductor and the capacitive component of the piezoelectric actuator substantially matches the resonant frequency of the internal R-L-C series resonant circuit of the piezoelectric actuator,

Wherein,

(I) Adjusting parameters of the internal R-L-C series resonant circuit of the piezoelectric actuator, and/or

(Ii) The boost circuit has an external capacitor in parallel with the capacitive component of the piezoelectric actuator,

So that the inductance of the external inductor is 30 muh or less.

18. The driving apparatus as claimed in claim 17, wherein,

19. The driving apparatus as recited in claim 18 wherein said voltage signal is applied to said first electrode and said second electrode to cause said end portion of said vibration element to perform an elliptical motion which is a combination of a vibration component in said axial direction and a vibration component perpendicular to said axial direction,

20. An electronic device, characterized in that the electronic device comprises a driving device according to any one of claims 1 to 19.

21. An electronic device, characterized in that the electronic device comprises a camera,

Wherein the camera comprises a drive device according to any one of claims 1 to 19,

The driving device is used for driving the lens unit of the camera attached to the driven element and used for automatic focusing.

22. The electronic device of claim 20 or 21, wherein the electronic device is a cell phone or a smart phone.

23. A method of controlling a piezoelectric actuator by a driver to drive a driven element in an axial direction, the piezoelectric actuator comprising:

A vibrating element in contact with the driven element and one or more sets of piezoelectric elements attached to the vibrating element;

Wherein the method comprises the following steps:

vibrating the vibration element by applying an oscillating voltage signal of the same frequency to the first electrode and the second electrode, thereby driving the driven element in contact with the vibration element in the axial direction,

The speed of the driven element is controlled by controlling the phase difference between the voltage signal applied to the first electrode and the voltage signal applied to the second electrode,

24. The method of claim 23, wherein applying the voltage signal to the first electrode and the second electrode imparts an elliptical motion to the end of the vibrating element, the elliptical motion being a combination of a vibration component along the axial direction and a vibration component perpendicular to the axial direction,

The controlling the speed of the driven element by controlling the phase difference includes controlling a vibration amplitude of the vibration component in the axial direction and a vibration amplitude of the vibration component perpendicular to the axial direction by controlling the phase difference.

25. A method according to claim 23 or 24, further comprising making the phase difference substantially zero so that the driven element speed is zero.

26. The method according to any one of claims 23 to 25, further comprising:

Gradually decreasing or increasing the phase difference from substantially pi at the beginning of driving the driven element from zero speed, and/or

The phase difference is gradually brought closer to approximately pi when the speed of the driven element is set to zero.

27. The method of claim 24, further comprising controlling the amplitude of the voltage signal applied to the first and second electrodes to compensate for amplitude variations of the vibration component perpendicular to the axial direction caused by the controlling of the phase difference.

28. The method of any one of claims 23 to 27, further comprising controlling the speed of the driven element by further controlling the frequency and/or amplitude of the voltage signals applied to the first and second electrodes.

29. A method according to any one of claims 23 to 27, further comprising controlling the speed of the driven element by controlling the frequency and/or amplitude of the voltage signal applied to the first and second electrodes, but not the phase of the voltage signal, when the speed of the driven element is equal to or greater than a predetermined value.

30. A computer program for causing a drive to perform the method according to any one of claims 23 to 29.

31. A computer readable storage medium, characterized in that the computer program according to claim 30 is stored on the computer readable storage medium.